On a cold Denver night in 2010, Steve Katsaros walked past a building under construction that was lit up like a Christmas tree by incandescent bulbs strung along each floor, all powered by a diesel generator. "I wondered about all the fuel being used and the pollution caused by keeping those lights on," he recalls. The next morning, Katsaros, then a patent agent at a law firm and a trained mechanical engineer, woke up and sketched a design for a solar-powered light bulb. Four days later, he filed for a patent.

When he researched potential markets, one opportunity leaped out at him: the 1.3 billion people around the world who live without electricity. Many burn kerosene lanterns for light, which not only pollute their environment but also endanger their homes and families with open flames and fumes. There's also the risk that children will ingest the cheap fuel, which costs around a dollar per liter.

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Katsaros named his company Nokero--as in: no kerosene--to appeal to such customers. He says the bulbs--which run on batteries powered by photovoltaic cells and shine for up to seven hours per charge--last three years and pay for themselves in a few weeks. Still, while many potential customers can find a dollar for a bit of fuel, they can't easily afford Nokero's lights, which run from $8 to $45. So Nokero sells (at wholesale prices) to nongovernmental aid organizations, which have distributed more than 1.3 million bulbs to communities in Haiti, Uganda, Cambodia, India, and elsewhere. About half of the company's sales go through the aid channel, while retail outlets account for the other half.

Last year, Nokero took in more than $2 million in revenue. Being a for-profit company, Katsaros says, is essential when helping people in "energy poverty." He can grow faster than a nonprofit, he says, which lets him make more bulbs and get them where they're needed quicker. "I want to prove to the world that the nonprofit strategy is too unscalable," says Katsaros, and that bringing a product to the world's poorest consumers can "grow something that changes the world."